Proteolytic enzymes have been used extensively in alkaline detergent formulations to aid in the removal of protein-based stains which tend to adhere to textile surfaces. The most common type of formulation, which employs enzymes of this nature, are solid based detergents. The enzyme in its solid stable form is mixed with alkaline solid detergent formulations containing the usual surfactants, anti-redeposition agents, water hardness control agents, other chelators and the like. Solid enzymes in this type of formulation have very reliable stability over extended periods. Hence, the solid enzyme based detergent products can be packaged and stored for extended periods before use.
There are, however, many cleaning situations where an enzyme based alkaline detergent is preferably in liquid form. Such liquid forms of detergents are more readily diluted and dispersed in the cleaning formulations. They are particularly useful in cleaning of textiles because they may be applied in concentrated liquid form before the normal cleaning process.
Considerable effort and interest has been pursued in formulating enzyme based cleaning systems which are in a liquid form. There is, however, a significant difficulty in maintaining enzyme activity in liquid based detergents. It is well known that cationic and the most common anionic surfactants attack enzymes, breaking them down and rendering them non-active. It is generally understood, however, that nonionic surfactants can be used in conjunction with enzymes and not appreciably affect the activity of the enzyme in a liquid formulation. It is also generally understood that the presence of water in a liquid enzyme formulation causes degradation of the enzymes by self-digestion which is commonly referred to as autolysis. The presence of oxygen in the liquid formulation can also present a significant problem because oxygen can denature the enzymes. The presence of oxygen is normally controlled by the use of antioxidants. However, the introduction of antioxidants to the composition can over time cause the pH of the composition to drop well below the normal alkaline pH range in which the enzymes are active. By virtue of the pH dropping, the enzymes become inactive.
However, in view of the significant interest in liquid detergents containing enzymes, several approaches have been taken to stabilize the enzyme composition so that the enzymes are active in use.
Enzyme detergent formulations have also become useful in clean-in-place operations where it is desired to remove protein-based deposits on various types of processing equipment such as dairy equipment. Quite often in dairy processing, high temperatures are used which results in the deposit of difficult to remove soils on internal surfaces of processing equipment. Removal is normally accomplished by the use of highly alkaline or highly acidic compositions. Such compositions, although successful in removing deposited materials, are somewhat hazardous to use and must be neutralized before being discarded. Furthermore, the highly alkaline or acidic cleaning compositions are very corrosive and can attack components of the processing equipment. Alternatives have therefore been sought.
U.S. Pat. No. 4,212,761 describes a composition which is useful in cleaning processing equipment in dairy production. The enzyme is particularly useful in dissolving milkstone deposits and other dairy deposits on interior surfaces of the processing equipment. The composition is very useful for a clean-in-place process; however, the composition is supplied in solid form and dissolved on site in water before use. Such solid composition consists essentially of a nonionic or anionic detergent, sodium carbonate or sodium bicarbonate and an alkaline protease. In solid form, the enzyme is stable even in the presence of the anionic detergent material. The nonionic or anionic detergent material is employed solely to act as a detergent to facilitate the cleaning action where it is thought that any suitable nonionic or anionic detergent material may be used. The preferred form of enzyme is a proteolytic enzyme which is capable of breaking down the deposited milk solids, particularly in the form of milkstone. Having to make up the composition on site significantly complicates the administration of the cleaning composition in a clean-in-place operation. Liquid formulations are far superior in this regard since they may be stored in drums and automatically dispensed as needed during the clean-in-place operation.
U.S. Pat. Nos. 4,243,543 and 5,064,561 recognize the advantages of liquid compositions for clean-in-place systems and describe two-part compositions which are kept separate until they are combined and diluted for use in the clean-in-place operation. U.S. Pat. No. 4,243,543 recognizes the significant problem in stabilizing enzymes in an aqueous system. In order to achieve such stabilization in an aqueous solution which may contain up to the perceived maximum of 30% by weight water, an antioxidant is used to enhance stability of the enzyme in the aqueous system. The enzyme-containing part of the composition comprises the proteolytic enzyme, an anionic and/or nonionic surfactant and the antioxidant with the balance being water. Because of the use of the antioxidant, the aqueous solution is not pH stable. The antioxidant will cause the pH of the solution to drop, thereby rendering the enzyme inactive over time. In order to maintain the pH of the composition in the desired range of 5.2 to 9 and avoid downward pH shifts, a buffering amount of a weak base is included to stabilize pH. The buffer may be any of the well-known compositions capable of stabilizing pH, such as carbonates which have a pKa within the range of about 6 to 12. In addition to further stabilize the enzyme in this composition, a water soluble polyol containing from 2 to 6 hydroxyl groups and having a molecular weight of less than 500 is used to achieve a stable composition for storage. The second component for this two-part cleaning system comprises a chelant or sequestering agent for sequestering the alkaline earth metal cations in the plant water used to dilute the two parts when combined during the clean-in-place operation.
U.S. Pat. No. 5,064,561 discloses a two-part clean-in-place system which provides for stability of the enzyme in the second concentrated solution by ensuring that the concentrate is substantially absent of free water and the enzyme is combined with a carrier such as alcohols, surfactants, polyols, glycols and mixtures thereof. The first concentrate comprises a hydroxide-based alkaline material, a defoamer, a solubilizer or emulsifier and a water hardness control additive. The defoamer is used to control foaming as caused by presence of the protease in the second concentrate. It is suggested, however, that the defoamer is optional if a liquid form of the enzyme is used in the second concentrated solution. However, the second concentrate still requires that the liquid form of the enzyme be absent of any free water as it Would apply to both the source of enzyme and carrier. Although this is a successful two-part clean-in-place system, it is difficult to supply the second concentrate containing the enzyme which is essentially absent of any free water.
It would therefore be beneficial if a two-part clean-in-place system particularly for use in cleaning dairy equipment could be made where water is present in the second concentrate containing the enzyme and where stability of the enzyme in the concentrate is maintained to ensure proper shelf life. provides two concentrates containing a minimum of